1. Field of the Invention
The present invention relates to an option fixing device which is coupled with an image forming apparatus, such as a copying machine, a printer and a facsimile machine, and fixes a toner image on a recording sheet discharged from the image forming apparatus.
2. Description of the Related Art
In fixing images of different image qualities, such as a color image and a black monochromatic image, or fixing images on different kinds of recording materials, such a normal paper and OHP, a common practice in an image forming apparatus according to a related art is to change a surface temperature of a heating roll or a rotation speed of fixing rolls (heating and pressing rolls). It is very difficult to change the picture quality, particularly gloss, by one fixing apparatus so as to satisfy a level of user""s liking on the picture quality. One of solutions for this difficulty is to use a plurality of fixing devices and to provide fixed images varied in picture quality.
The following technique (J01) has been known for this type of fixing device.
Technique disclosed in (J01) JP-A-11-242400
This publication proposes that a plurality of fixing devices are provided to produce an image of high gloss level, which resembles a photograph image. One of those fixing devices is a belt fixing device. This belt fixing device is detachably attached to the image forming apparatus.
In the technique where the plurality of fixing devices are used to increase a variation of picture quality, as in the related art (J01), the image forming apparatus is indispensably provided with a sheet-discharging transport path for transporting a normal recording sheet having undergone the fixing process, a transport path for transporting the normal fixed recording sheet to a second fixing device, and a path selector.
Since the image forming apparatus must be provided with the sheet-discharging transport path for transporting a normal recording sheet having undergone the fixing process, the transport path for transporting the normal fixed recording sheet to a second fixing device, and the path selector, the image forming apparatus is complicated in construction and increased in size, and hence increased in cost.
For the above background reasons, objects of the present invention as follows:
enabling an image forming apparatus incapable of fixing a gloss toner image to form a gloss toner image; and providing an option fixing device which can fix, as desired, a toner image of a recording sheet discharged from the normal sheet discharge port of the image forming apparatus.
Description of the invention, which succeeds in solving the problems mentioned above, will be given hereunder. In the description, constituent elements of the invention will be attached with reference symbols parenthesized for ease of their correspondence to those in the embodiment description to be given later. It should be understood that the reference symbol are used for ease of better understanding of the invention, and the use of them does not limit scope and spirits of the invention.
To achieve the above object, there is provided an option fixing device (U3) according to the first aspect of the invention, comprising:
a sheet entrance port (2a) through which a recording sheet (S) is entered;
a discharge port (3a, 4a; 3b) adapted to discharge the recording sheet (S);
first (SH6) and second sheet transport paths (SH7) adapted to transport the recording sheet (S) entered to the discharge port (3a, 4a; 3b);
a transport path switch member (G3) being movable between a first switch position for transporting the recording sheet (S) to the first sheet transport path (SH6) and a second switch position for transporting the recording sheet (S) to the second sheet transport path (SH7);
a fixing unit (F) adapted to heating-fix a toner image on the recording sheet (S) transported through the second sheet transport path (SH7); and
a switch member drive member (SL) adapted to move the transport path switch member (G3) to one of the first and second switch positions in accordance with a transport path switch signal,
wherein the option fixing device (U3) is detachably coupled to an image forming apparatus (U1) in which the toner image is transferred onto the recording sheet (S), the toner image is fixed onto the recording sheet (S), and the recording sheet (S) is discharged from a sheet discharge port (Ka) of the image forming apparatus; and the recording sheet discharged from the sheet discharge port of the image forming apparatus is entered through the sheet entrance port.
In the option fixing device according to the first aspect of the invention, comprising the above described structure, a recording sheet (S) discharged from the image forming apparatus (U1) is transported to the sheet entrance port (2a) in a state where the option fixing device (U3) is coupled to the image forming apparatus (U1). The switch member drive member (SL) drives the path switch member (G3) to the first switch position or the second switch position in accordance with the transport select signal.
The path switch member (G3), when moved to the first switch position, guides the recording sheet (S) entered through the sheet entrance port (2a) to the sheet discharge port (4a; 3b), while not guiding a recording sheet (S) to the fixing unit (F).
The path switch member (G3), when moved to the second switch position, guides the recording sheet (S) entered through the sheet entrance port (2a) to the second sheet transport path (SH7). The second sheet transport path (SH7) guides the recording sheet (S) entered through the sheet entrance port (2a) to the fixing unit (F), and then to the sheet discharge port (3a; 3b).
The toner image on the recording sheet transported through the second sheet transport path (SH7) is fixed at a fixing rate appropriately preset. Thus, the resultant toner image has a good gloss.
The option fixing device according to the first aspect of the invention can fix, as desired, the toner image on the recording sheet (S) discharged from the sheet discharge port (Ka), usually used, in the image forming apparatus (U1) Further, the option fixing device according to the first aspect of the invention enables an image forming apparatus incapable of fixing a gloss toner image to form a gloss toner image.
In the second aspect of the invention, there is provided the option fixing device according to the first aspect of the invention, wherein the fixing unit (F) is a belt type fixing unit having a fixing belt (Bt) adapted to heating-fix the toner image on the recording sheet (S) transported through the second sheet transport path (SH7).
The option fixing device according to the second aspect of the invention comprising the above described structure can produce a toner image with a good gloss because of using the fixing unit (F) having a fixing belt (Bt)
In the third aspect of the invention, there is provided the option fixing device according to any one of the first and second aspects of the invention, further comprising: a sheet transporting speed control section (C2) adapted to control a sheet transporting speed to change a sheet transport speed at the time the recording sheet (S) passes through the fixing unit (F) of the second sheet transport path (SH7) to a sheet transport speed being slower than a sheet transport speed at the time the recording sheet (S) is entered, the sheet transport speed at the time the recording sheet (S) passes through the fixing unit (F) corresponds to a fixing rate for forming a gloss image.
In the option fixing device (U3) according to the third aspect of the invention comprising the above described structure, the sheet transporting speed control section (C2) controls a sheet transporting speed such that when the recording sheet entered through the sheet entrance port (2a) passes through the fixing unit (F) of the second transport path (SH7), the control section (C2) decreases the sheet transporting speed to a speed which is slower than that when the recording sheet (S) is entered to the sheet entrance port (2a) so that the sheet transporting speed corresponds to a fixing rate for forming a gloss image. Accordingly, the option fixing device (U3) according to the third aspect of the invention can adjust the sheet transporting speed of the recording sheet (S) entered through the sheet entrance port (2a), independently of the sheet transporting speed of the recording sheet (S) passing through the fixing unit (F). Specifically, the option fixing device (U3) according to the third aspect of the invention can set the sheet transporting speed of the recording sheet (S) entered through the sheet entrance port (2a) in connection with a sheet discharging speed of the recording sheet (S) discharged from the image forming apparatus (U1) . Accordingly, the image forming apparatus (U1) can control a sheet transporting speed at the time of forming an image, while not taking the sheet transporting speed of the option fixing device (U3) according to the third aspect of the invention into account.
In the fourth aspect of the invention, there is provided the option fixing device (U3) according to any one of the first to third aspect of the invention, wherein a sheet transport distance between an discharge roll (Rh) of the image forming apparatus (U1) and the fixing unit (F) of the second sheet transport path (SH7) is longer than a length of the recording sheet (S) having the maximum size to be used in a transport direction.
In the option fixing device (U3) according to the third aspect of the invention comprising the above described structure, after the rear end of the recording sheet (S) passes the discharging roller (Rh), the forward end of the recording sheet (S) reaches a fixing region (Q5) of the fixing unit (F). Accordingly, the sheet transporting speed of the third option fixing device (U3) may controlled in the following way. (1) The sheet transporting speed of the option fixing device (U3) is set to be equal to that of the image forming apparatus (U1) till the rear end of the recording sheet (S) pass through the discharging roller (Rh), and whereby the recording sheet (S) is reliably and smoothly discharged from the image forming apparatus (U1) to the option fixing device (U3). (2) After the rear end of the recording sheet (S) passes through the discharging roller (Rh) and before the forward end of the recording sheet reaches the fixing region (Q5) of the fixing unit (F), the sheet transporting speed is decreased to a sheet transporting speed corresponding to a desired fixing rate.
In the fifth aspect of the invention, there is provided the option fixing device (U3) according to any one of the first to fourth aspects of the invention, further comprising a sheet sensor (SN1) adapted to detect a forward end of the recording sheet (S), disposed near a fixing region (Q5) provided in an upstream side of the fixing unit (F) with respect to a sheet transporting direction.
In the option fixing device according to the fifth aspect of the invention comprising the above described structure, the sheet sensor (SN1) detects the forward end of the recording sheet (S) at an upstream position as view ed in the sheet transporting direction before the recording sheet (S) reaches the fixing region (Q5) of the fixing unit (F) . Accordingly, the detection is possible as to whether or not the rear end of the recording sheet (S) passes through the discharging roller (Rh) of the image forming apparatus (U1), on the basis of a detection signal of the recording sheet (S).
After the rear end of the recording sheet (S) passes through the discharging roller (Rh) of the image forming apparatus (U1), the sheet transporting speed in the option fixing device (U3) is decreased to a sheet transporting speed corresponding to a fixing rate at which a gloss image is formed.